1. Field of the invention
This invention relates to an optical disc device capable of coping with plural types of optical discs, and a method for discriminating between plural types of optical discs.
2. Description of Related Art
As optical discs are in widespread use, optical discs of the compact disc CD type are used in many fields, including the field of musical applications. The CDs for music are usually designed as replay-only media. However, an overwrite type disc termed compact disc recordable (CD-R) is also commercialized.
On the other hand, an optical disc termed a digital versatile disc/digital video disc (DVD) has also been developed as an optical disc suitable for multimedia use. This DVD is proposed as being adaptable to a wide field of applications, such as for use with video data, audio data or computer data. The DVD, which is an optical disc of the same size as the CD (12 cm in diameter), has a significantly increased recording capacity.
Meanwhile, in keeping pace with the development of a new optical disc, it becomes desirable to provide an optical disc device that is also compatible with a conventional optical disc.
As for the DVD, it is desirable to develop an optical disc device capable of coping with both the CD and the DVD. However, since the CD and the DVD differ in reflectivity depending on, for example, a difference in the structure of the signal recording layer of the optical disc, the RF signals obtained by an optical pickup are varied in signal level, depending on the optical disc type, whilst optimum values of parameters of various servo systems, such as focussing servo or tracking servo systems, are also changed.
Therefore, an optical disc device, adapted for coping with plural optical disc types, is required to correctly discriminate the type of the optical disc on loading the optical disc thereon.
If the disc is of the type in which an optical disc is housed in a cartridge, the disc type can be easily discriminated by providing a cartridge discriminating hole. However, if the optical disc is not of the type housed in a cartridge, and moreover the optical disc itself is of the same size, this mechanical discrimination system cannot be used.
Moreover, if special components or units are provided for discriminating the disc type, such as a sensor, the device is undesirably complicated in structure, while the manufacturing costs are also raised.